A Study on the Joint Probability of Waves and Water Levels

• Main Authors: Chih-chiang Chang, 龔志富
• Other Authors: Chia Chuen KAO
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/70386708543838256775

碩士 === 國立成功大學 === 水利及海洋工程學系專班 === 96 === Waves and water levels are the important factors of inundation in coastal area. Currently, Sea dike is the most important sea defenses in coastal area of Taiwan. The deterministic height of a dike will be much concerned to the success or failure for designed dike. Generally, the deterministic value of a dike height will be a linear accumulation value to the oceanic parameters of designed wave height, astronomical tide level and storm surge, i.e., the maximum wave height and the maximum water level will be considered to happen in a same time. This paper is a study to utilize the analytic approach of joint probability to probe into the recurrent probability of waves and water levels. Meanwhile, it will also make a comparison with the result of traditional analytic approaches. Survey stations which contain the wave height and the water tide level records in a same time will be selected one each from the eastern, southern, western and the northern of Taiwan respectively in this paper. Taking into account the mainly reason of dike’s damage due to typhoon in Taiwan, the analytic objective will be restrictedly focused on the maximum wave and the maximum water levels during the typhoon attacked period. In order to getting the adequate data from the field, it will assume that the observed data of each station and typhoon would be independent each other respectively. All the data will be combined into one group of wave height and water level versus the time series. So 111 typhoons data are obtained and there are 7,440 groups of data totally. The analytic result shows that the maximum wave height is a Weibull Distribution during the typhoon period and the maximum water level fits the Extreme Type I Distribution. The wave height and water levels in each recurrence period’s year will be derived via the frequency analysis. After Comparing with the result of Joint probability - wave heights and water levels, the total designed water level of traditional frequency analysis is towards conservative. Under the same condition, the analytic result of Joint probability is higher than the result of traditional frequency analysis. Besides, method for the uncertainty analysis of Joint probability of waves and water levels is the Mote Carlo Simulation which is utilized to simulate numerous and repeated data in the paper. The coefficient of variation is an index of measure for the uncertainty analysis. The analysis result shows, under the condition of similar data quantities, the uncertainty index counting up from the simulation data is lower than the one counting up from the observation data of field. It means that a stable and reliable wave height or water level will be deterministic via the simulation of numerous data. Simultaneously, accuracy for the result of simulation will be confirmed via a collection of numerous data of field. In accordance with the result of quantity analysis, the coefficient of variation of waves or water levels which is derived from the joint probability of waves and water levels will be less than 10 % when the quantities of simulating data are exceeded in 1,000. So this result can be a reference for the collecting data of field hereafter.